The present invention generally relates to methods and systems for depositing thin films, and more particularly, to methods and systems for depositing thin magnetic films.
Magnetic films are used in many diverse applications. Some applications include, for example, data storage applications such as Magnetic Random Access Memories (MRAM), magnetic disk memories, magnetic tape storage systems, magnetic strip readers, etc. Other applications include magnetic sensor applications. In each of these applications, a magnetic film in some form is typically used. The magnetic film can include a single layer or multiple layers. To provide the desired functionality, some magnetic films include both magnetic and non-magnetic layers, and sometimes metallic and non-metallic (e.g. dielectric) layer. For example, in MRAM applications, AMR, Giant MagnetoResistive (GMR), and sometimes Colossal MagnetoResistive (CMR) films are used. One such MRAM magnetic film is shown and described in U.S. Pat. No. 5,569,617 to Yeh et al.
A number of process techniques are currently used to form magnetic films, including Molecular Beam Epitaxy (MBE), Plasma Vapor Deposition (PVD) and Ion Beam Deposition (IBD). MBE is useful for depositing layers at very low energy, which can produce pseudo epitaxial layers. PVD is useful for depositing layers at a higher energy, which can produce layers that have, for example, good current carrying capabilities. IBD is useful for depositing layers at still higher energy and reduced pressures, which can produce layers with higher crystallinity. To date, however, long throw magnetrons have not been used to form magnetic films to considerable disadvantage.
The present invention provides methods and apparatus for depositing a magnetic film using one or more long throw magnetrons, and in some embodiments, an ion assist source and/or ion beam source. The long throw magnetrons can deposit particles at low energy and low pressure, which can be used to, for example, deposit interfacial layers or the like. In some embodiments of the present invention, an ion assist source is also used with the long throw magnetrons to increase the energy of the particles provided by the long throw magnetrons, and/or modify or clean the layers on the surface of the substrate. An ion beam source may also be used, sometimes separately from the long throw magnetrons and/or ion assist source and other times in conjunction therewith. The ion beam source can be used to deposit layers at a higher energy and lower pressure to, for example, provide layers with increased crystallinity. By using a long throw magnetron, an ion assist source and/or ion beam source together or separately, certain magnetic films can be advantageously provided.
In one illustrative embodiment, a vacuum chamber is provided with one or more long throw magnetrons therein. Each magnetron has a magnetron target. The substrate is held in place by a substrate carrier that is spaced a long throw distance from the one or more long throw magnetrons. This spacing helps keep the substrate out of the high energy plasma region produced by the long throw magnetrons, and also reduces the magnetic field in the vicinity of the substrate that is produced by the long throw magnetrons. Both of these can be important when making high grade magnetic films. Each long throw magnetron preferably produces ions that are directed to a corresponding magnetron target, which then sputters particles from the corresponding magnetron target to the substrate to form one or more magnetic layers. The one or more magnetrons may be activated together or separately, depending on the application.
Because some magnetic films, such as GMR films, include layers that are formed from several different materials, it is contemplated that selected magnetron targets may be formed from different material systems. By selecting an appropriate magnetron, a desired material can then be deposited on the substrate. By sequencing the various long throw magnetrons, a desired sequence of layers can be deposited.
It is recognized that some layers may require a mixture of target materials. For these layers, two or more magnetrons may be in activation simultaneously. For example, activating three magnetrons, one with Ni target, another with a Co target, and yet another with a Fe target, a NiCoFe permalloy layer may be deposited. The relative concentration of each target material can be controlled by controlling the power that is provided to each magnetron. The relative power can control the deposition rate of each constituent target material. It is contemplated that the relative concentration of the target materials can be homogenous or inhomogeneous through the deposited layer, as desired.
Long throw magnetrons are well suited for depositing materials at low energy and low pressure, which can be particularly useful in depositing interfacial layers or the like. For higher energy deposition, however, it is contemplated that an ion assist source may also be provided in the vacuum chamber. The ion assist source can provide assist ions in and around the substrate. The assist ions can be used for a variety of purposes, including for example, adding energy to the particles provided by the one or more long throw magnetrons, cleaning and/or modifying a layer that is deposited by the one or more of the long throw magnetrons, etc. The ion assist source can be activated before, during, or after the one or more long throw magnetrons are activated, depending on the application at hand. In addition, multiple ion assist sources can be provided if desired.
To deposit layers at even a higher energy, an ion beam source may be provided. As is known, ion beam deposition can provide higher energy deposition at lower pressures, which for some materials, can increase the crystallinity of the layer. In a preferred embodiment, the ion beam source is used to produce layers or portions of layers that are more suited to ion beam deposition. The ion beam source can be activated before, during, or after the one or more long throw magnetrons are activated, and/or before, during, or after the ion assist source is activated, depending on the application at hand. In addition, multiple ion beam sources may be provided, if desired.
For some applications, it may be desirable to set a magnetic direction of one or more of the layers of the magnetic film. To accommodate this, a magnetic field source may be provided near the substrate. In some embodiments, the magnetic field source is activated to provide a setting magnetic field at the substrate, preferably during the deposition of selected layers of the magnetic film.